"On the Linux kernel mailing list, Willy Tarreau has announced that there will be no more releases for version 2.4 of the Linux kernel. Tarreau, who is responsible for maintaining the Linux 2.4 kernel, said that 'few people' still use this version. According to him, these users are better served by a central Git repository that collects bug fixes and that he has now created such a repository for them." I remember when 2.4.0 was released... Proper USB support! Them were the days.

The move to stop releasing 2.4 updates seems reasonable. I don't think any distributions still support the 2.4 kernel. Even Red Hat's RHEL supported line I think uses 2.6 these days. If there is anyone out there still actively using 2.4 they're probably already familiar with compiling and updating legacy software.

RHEL 4 went EOL (technically End of Production according to https://access.redhat.com/support/policy/updates/errata/) on February 29, 2012. It's now only receiving critical impact security fixes if you pay for a special Extended Life Cycle Support subscription above and beyond the normal RHEL subscription.

Both CentOS and Scientific Linux ended their 4.x lines on February 29. So, for all intents and purposes, RHEL 4 is publicly End Of Life.

Things like cable box and other "black boxes", hardware made by a manufacturer (pace, sci. atlanta), supported by another (cable company) and installed in yet another (private house or business) are a different story. There is still tons of OS/2 and early Linux (2.2, 2.4). You know, the kind of (sometime large) niches that recently stockpiled 80386 processors to be sure they would have enough of them for the next 30 years.